The present invention relates to a compressed-air supply device for commercial vehicles
In modern commercial vehicles, pneumatic systems such as compressed-air brakes are frequently used. In order to supply such pneumatic systems with compressed-air, compressed-air supply devices are employed which generally have an electronic control device. In order to be able to selectively actuate valves of the compressed-air supply device via the electronic control device, the valves are frequently embodied as solenoid valves. This makes it possible to carry out precise control of the compressed air made via a compressor and to regenerate the air filter. In order to ensure the compressed-air supply for such an important system as brakes in the event of failure of the electronic control device, for example as a result of a faulty power supply or because of failure of a sensor, a fall-back level is generally made available which functions even without an electronic control device. However, the possibility of selective actuation of the valves is then also eliminated. For example, without an electronic control device the compressor can no longer be placed in an energy saving mode if an operating pressure of the compressed-air supply device is reached. This can lead to a situation in which the compressor continues to work against a high pressure over a long time until a safety valve releases the pressure at a maximum pressure. This can lead to considerable loading of the compressor, which can even damage the compressor, for example due to overheating. When the electronic controller fails, it is generally no longer possible to regenerate the air filter. As a result there is a risk of the air filter and downstream consumer systems, in particular the brake systems, being operated under wet conditions.
An object of the present invention is to make available, in an electronically controlled compressed-air supply device, a fall-back level which permits improved operation, in particular of the compressor, and of the regeneration, in a purely pneumatic fashion.
According to the invention, a compressed-air supply device is provided for commercial vehicles, wherein the compressed-air supply device is or can be connected electrically to an electronic control device. The compressed-air supply device has at least one control valve which can be actuated via the electronic control device. The control valve has at least one inlet connection, one venting connection and one outlet connection. In addition, the compressed-air supply device has a control line which is connected to the outlet connection of the control valve, wherein the control line is or can be connected to a control inlet of a compressor and/or an inlet of a regeneration valve, as well as a supply line via which compressed air is or can be guided to the inlet connection of the control valve, and a venting line which is connected to the venting connection of the control valve, wherein the control valve can be vented via the venting line. The control valve is also embodied in such a way that when there is a predetermined opening pressure in the supply line, said control valve pneumatically brings about a fluid-conducting connection between the inlet connection and the outlet connection in such a way that the control line is ventilated. Bringing about a fluid-conducting connection between the inlet connection and the outlet connection on the basis of the opening pressure in the supply line can generally be referred to as pneumatically opening the control valve. In particular, it is possible to provide that the control valve is embodied in such a way that the fluid-conducting connection between the inlet connection and the outlet connection is brought about independently of the actuation by the electronic control device. It is therefore possible to bring about, via the control valve which is otherwise controlled via the electronic control device, a pressure buildup in the control line by purely pneumatic means if the pressure in the supply line reaches or exceeds the opening pressure. The actuation of the control valve by the electronic control device can be carried out in an indirectly or directly electrical fashion, for example by energizing electromagnetic components of the valve. The control valve can be embodied, in particular, as a solenoid valve. It is also conceivable for the control valve to have, in addition to a pneumatic valve, a solenoid valve component for performing pilot control of the pneumatic valve, which solenoid valve component is actuated by the electronic control device. The control valve can be embodied as a 3/2-way valve. In a normal position, the control valve can be switched in such a way that it connects the control line to the venting line, that is to say in such a way that there is a fluid-conducting connection between the outlet connection and the venting connection. The inlet connection and therefore the supply line can be shut off in the normal position. It is therefore possible for the control line to be vented or being capable of being vented in the normal position. In an on position, the control valve can be switched in such a way that said control valve connects the control line in a fluid-conducting fashion to the supply line and shuts off the venting line. As a result, the inlet connection and the outlet connection are connected to one another in a fluid-conducting fashion and the venting connection is shut off. The electronic control device can permit the control valve to be switched over between the normal position and the on position. It may be expedient to embody the control valve in such a way that it assumes the normal position if it is not actuated via the electronic control device and/or not energized. For this purpose, it is possible to provide, for example, a resetting device, such as a spring arrangement, which prestresses the control valve into the normal position. The control valve can be embodied in such a way that in or out of the normal position and/or when it is not energized it pneumatically opens given a predetermined opening pressure in the supply line, with the result that the control line is ventilated. It is conceivable that when the control valve pneumatically opens owing to the opening pressure in the supply line the control valve is not completely switched into the on position but instead assumes an intermediate position which is referred to as an open position. The pneumatic opening can therefore also be referred to as switching into the open position. It may be the case, for example, that in the open position the venting connection is not shut off or not shut off completely. The electronic control device can be considered to be part of the compressed-air supply device or be embodied so as to be separate therefrom. The compressed-air supply device can comprise the compressor or be considered to be a separate or separable device from the compressor. The control line can be connected or be capable of being connected, in particular, to a compressor control inlet via which the compressor can be actuated pneumatically. It is conceivable, for example, that when a pressure is present at the control inlet of the compressor, said compressor switches into an energy saving mode. In an energy saving mode, the compressor can, for example, be decoupled from a drive or a shaft, or switched off. If there is no pressure at the control inlet of the compressor, the compressor can be operated in such a way that it supplies compressed air for the compressed-air supply system. The supply line can be employed, in particular, to distribute compressed air to consumer systems such as, for example, brakes, an air suspension system, a trailer or the like. A regeneration valve may be a valve via which regeneration of an air filter of the compressed-air supply system takes place and/or is controlled. In particular, a nonreturn valve in a regeneration line can be considered to be a regeneration valve. The air filter may be part of the compressed-air supply system. It is conceivable, in particular, that the compressed-air preparation device has a second control valve, which is embodied in a way analogous to the control valve and has a predetermined, second opening pressure. The second control valve can generally have the properties and features mentioned for the control valve.
The second opening pressure can correspond to the first opening pressure or be the same as said pressure. It can be expedient if the second opening pressure differs from the first opening pressure. In particular it is possible to provide that an inlet connection, referred to as a second inlet connection, of the second control valve is or can be connected to the control line, which in this case then acts as a supply line for the second control valve. In this context, the second control valve can be, in particular, a regeneration valve. As a result, the second control valve can be switched pneumatically into its open position if the control valve is in the open position. It may be advantageous if a first control valve is or can be connected via its control line to a compressor control inlet and to the second inlet connection of a second control valve which is employed as a regeneration valve. Within the scope of this description, a connection or fluid-conducting connection between two pneumatic components or a line and a pneumatic component such as a valve constitutes a pneumatic connection, with the result that compressed air can be guided via the connection. A commercial vehicle may be, in particular, a truck or a mobile implement, such as, for example, a tractor. A rail vehicle can also be considered to be a commercial vehicle. Generally, it may be expedient if the predetermined opening pressure and/or, if appropriate, the second opening pressure is higher than an operating pressure of the compressed-air supply device. The operating pressure can be predefined and/or monitored by the electronic control device. For example, the electronic control device can be designed to stop the compressed-air supply, for example by switching the compressor into its energy saving mode, when the operating pressure is reached. It is possible to provide that the electronic control device senses the pressure in the compressed-air supply device at one or more locations by means of suitable sensors, and switches off or disconnects the compressor when the desired operating pressure is reached. For this purpose, a suitable solenoid valve can be actuated in order to input a pressure signal into the compressor control line. The solenoid valve can be considered to be a control valve as described above. An operating pressure may be, for example, approximately 12 or 12.5 bar. The operating pressure may be determined, in particular, in the supply line. For example, the opening pressure can be between 13 bar and 14 bar, for example 13 bar, 13.5 bar or 14 bar. In order to protect the compressed-air supply device it is possible to provide a maximum safety pressure which the device must not exceed under any circumstances. In order to prevent this safety pressure from being exceeded, a safety valve can be used which, in the event of the safety pressure being exceeded, brings about venting to the atmosphere. The opening pressure and/or, if appropriate, the second opening pressure are/is expediently below this safety pressure. As a result, the opening pressure of a control valve can be between the operating pressure and the safety pressure. It is also conceivable that the conventional safety valve is replaced by the control valve. This is because it is possible to ensure pneumatically that the opening pressure is not exceeded if the control line which is coupled to the described control valve is connected for switching the compressor and/or for discharging pressure, for example to a means for venting to the atmosphere or a discharge valve for a venting means, or by initiating a regeneration process. In this case, the opening pressure can therefore be considered to be a safety pressure. In the scope of this description it is also possible for the minimum flow cross section to be considered in each case as an effective flow cross section in a line, connection or in a valve, said minimum flow cross section, in the case of the flow under consideration, plays a role which is relevant to the flow. The opening pressure of a control valve can be set by suitably configuring the valve, for example by correspondingly setting a spring arrangement.
The compressed-air supply device can be embodied in such a way that a venting flow cross section which has the function of venting the control valve is smaller than a control flow cross section which has the function of ventilating the control line via the control valve. It is therefore possible to ensure that even when the control valve is in an intermediate position through pneumatic actuation via the supply line, a pressure buildup can reliably take place in the control line in that the venting connection, inlet connection and outlet connection are connected to one another in a fluid-conducting fashion. Generally, the flow cross sections which are effective for certain flows in the associated valve and/or in associated lines can be set or defined. During the setting of the flow cross sections it is generally possible to take into account the opening pressure and its effects on the cleared opening of the outlet connection and venting connection.
In one development it is possible to provide that a supply flow cross section which has the function of guiding compressed air into the control valve via the supply line and the inlet connection is larger than a venting flow cross section which has the function of venting the control valve and/or than a control flow cross section which has the function of ventilating the control line via the control valve. As a result, a sufficient amount of compressed air can be fed via the supply line to prevent excessive venting via the venting connection and the venting line. Sufficiently large pressure buildup can also be achieved by ventilating the control line. The flow cross section which is effective for the supply of air via the inlet connection can be made as large as or larger than the sum of the flow cross sections which have the function of performing ventilation via the venting connection and the pressure buildup via the outlet connection.
In particular, a restrictor, which can define a minimum flow cross section for venting via the venting connection, can be provided in the venting line. As a result, a suitable effective venting flow cross section can be defined easily without having to make a change to a conventional control valve.
It is possible to provide that a flow cross section of the venting connection which has the function of venting the control valve is smaller than the flow cross section of the control connection which has the function of ventilating the control line via the control valve. In this way it is possible to ensure that the desired flow conditions are already defined by the control valve independently of a routing of a line.
It is conceivable that a flow cross section, which has the function of guiding compressed air into the control valve, of the inlet connection is larger than a flow cross section, which has the function of venting the control valve, of the venting connection and/or a flow cross section, which has the function of ventilating the control line via the control valve, of the outlet connection. It is therefore possible to ensure simply by suitable dimensioning of the connections of the control valve that a pressure buildup in the control line is possible in the fall-back mode. The flow cross section which has the function of supplying air via the inlet connection can be made as large as or larger than the sum of the flow cross section, which has the function of venting, of the venting connection and the flow cross section, which has the function of building up pressure, of the outlet connection.
In the control line it is also possible to provide a quick-acting venting valve. Such a quick-acting venting valve can permit, in particular, more rapid venting of the control line than would be possible via the control valve. In this context, it is possible to provide that venting via the quick-acting venting valve is triggered by switching the control valve from the open position into the normal position, during which switching a fluid-conducting connection is brought about between the inlet connection and the venting connection of the control valve and/or the connection between the inlet connection and the outlet connection is interrupted. Generally, a quick-acting venting valve can be a 3/2-way valve. A valve can generally be considered to be a quick-acting venting valve which has an inlet connection, an outlet connection and a venting connection. In the case of a quick-acting venting valve the outlet connection can be vented via the venting connection when the inlet connection is vented. If the inlet connection is ventilated, the quick-acting venting valve can connect the outlet connection to the inlet connection and shut off the venting connection.
It may be expedient if a flow cross section, which has the function of venting the control line via the quick-acting venting valve, is larger than a flow cross section, which has the function of venting the control valve via the venting line. This ensures that rapid venting can take place via the quick-acting venting valve.
The control valve can be embodied in such a way that when there is a predetermined closing pressure in the supply line, said control valve interrupts a fluid-conducting connection between the inlet connection and the outlet connection is brought about. In particular it is possible to provide that in the case of a drop in the pressure in the supply line as far as the closing pressure this fluid-conducting connection is interrupted after the control valve has pneumatically opened. The control valve can therefore switch pneumatically from the open position into another position, preferably into the normal position, as a function of the pressure in the supply line. The interruption of the connection between the inlet connection and the outlet connection can occur, in particular, when the control valve is in the currentless state or actuation by the electronic control device does not take place. Generally, the closing pressure of a control valve can be set by a suitable configuration of the valve, for example by a spring arrangement being correspondingly set.
It is conceivable that the control valve is embodied in such a way that, when a predetermined closing pressure in the supply line is undershot, said control valve brings about a fluid-conducting connection between the outlet connection and the venting connection. It is therefore possible for venting of the control line to take place or to be initiated via the control valve.
The closing pressure can be lower than the opening pressure. In this context, the control valve can, in particular, be set in such a way that it has a hysteresis. It is therefore possible to define a pressure range in which the control valve is pneumatically opened in order to relieve the compressor for as long as possible. The closing pressure can be below the operating pressure or approximately in the region of the operating pressure.
Of course, the specified features for a control valve can also analogously apply to a second control valve which is possibly present and which has a second opening pressure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.